Direct bath smelting process with peripheral cold zone management at the metal-slag interface

Abstract

An improved direct smelting vessel includes a smelting reduction vessel (SRV) and, optionally, a cyclone converter furnace (CCF). The SRV provides a means for promoting metal mixing in a zone below the slag layer adjacent the vessel wall of the direct smelting vessel. The means for promoting metal mixing may include a split-level refractory hearth having two refractory bed levels, a refractory hearth having one or more gas bubbling devices, and / or at least one pair of solid injection lances (or other means) for alternating solid injection at any one time. The means for promoting metal mixing reduces stagnant areas that can support a semi-solid slag layer that limits metal-to-slag heat transfer. The means for promoting metal mixing maintains an effective temperature difference of 40°C or less between the tapped metal from the forehearth and the metal at the vessel wall.

Description

[Technical Field]

[0001] [Priority claim] This application claims priority to U.S. Provisional Application No. 63 / 352,492, entitled "A Direct Bath Smelting Process with Management of Peripheral Cold Zones at the Metal-Slag Interface," filed June 15, 2022, and U.S. Nonprovisional Patent Application No. 18 / 204,683, entitled "A Direct Bath Smelting Process with Management of Peripheral Cold Zones at the Metal-Slag Interface," filed June 1, 2023, each of which is assigned to the present assignee and is incorporated herein by reference in its entirety.

[0002] The present invention relates to a method and apparatus for the direct smelting of metalliferous materials. [Background technology]

[0003] Two known methods for direct smelting of metalliferous materials that primarily use a molten bath as the smelting medium are commonly referred to as HIsmelt and HIsarna. Summary of the Invention

[0004] The present invention relates to an improved direct smelting vessel comprising a smelt reduction vessel (SRV) and, optionally, a cyclone converter (CCF). In particular, the direct smelting vessel may be a roofed, enclosed vessel comprising a refractory hearth region at the bottom of the vessel for containing a molten bath and a gas region between the molten bath and the roof. Means are provided for promoting metal mixing (e.g., passive mixing and / or active mixing) in a zone adjacent the vessel periphery at the metal-slag interface (e.g., a cold shoulder zone). For example, providing improved metal mixing in this zone reduces stagnant regions that can support a semi-solid slag layer that limits metal-slag heat transfer. In particular, the means for providing metal mixing maintains an effective temperature difference between the forehearth tap metal and the metal at the vessel wall of 40°C (72°F) or less.

[0005] In one embodiment of the present invention, the means for facilitating metal mixing may comprise a split-level refractory hearth having two refractory bed levels, a refractory hearth utilizing one or more gas bubbling devices, and / or at least a pair of solids input lances, wherein a first opposing lance of the pair delivers all of the input solids at any time before (e.g., immediately or after a period of time) a first opposing lance of the pair switches over to a second opposing lance of the pair.

[0006] For a split-level refractory hearth, this means includes a main level having a depth that improves molten metal mixing, which plays an important role in relation to metal-slag heat transfer. Additionally, the SRV includes a secondary level having a different depth (e.g., deeper than the depth of the main level) that provides a safety function related to preventing slag from being discharged into the forehearth. The depth of the split-level refractory hearth is described in further detail herein.

[0007] For refractory hearths utilizing one or more gas bubbler devices, the gas bubblers promote metal convection by injecting gas (e.g., argon) into a zone below the slag layer adjacent the vessel wall of the direct smelting vessel.

[0008] For at least one pair of solid injection lances, the injection lance provides an injection jet of sufficient strength to promote metal convection at the opposing vessel wall. Alternating with opposing lances (e.g., for a given pair of lances) in a regular cycle based on the time it takes for the hot metal adjacent the vessel wall to cool may be used to promote metal convection that limits the formation of a semi-solid slag layer at the metal-slag interface.

[0009] It should be understood that other means (either passive or active) for promoting metal intermixing adjacent to the metal wall may be utilized to reduce the semi-solid slag layer described herein.

[0010] One embodiment of the present disclosure includes a method for directly smelting a metalliferous material in a direct smelting vessel to produce molten metal. The method includes charging solid carbonaceous material through at least one charging lance extending into the direct smelting vessel, such that the solids at least partially penetrate a layer of molten metal in the direct smelting vessel, the layer of slag floating thereon. The method further includes promoting metal mixing in a zone immediately below the slag layer adjacent a vessel wall of the direct smelting vessel.

[0011] According to one embodiment, metal mixing reduces the volume occupied by stagnant regions of low temperature sufficient to support a semi-solid slag layer that limits metal-slag heat transfer.

[0012] In yet another embodiment, metal mixing maintains an effective temperature difference between the tapped metal in the forehearth and the metal at the vessel wall of 40° C. or less.

[0013] In yet another embodiment, metal mixing is promoted using a direct smelting vessel with a split-level refractory bed having two refractory bed levels, including a first level having a first depth supporting a first metal depth and a second level having a second depth supporting a second metal depth, the second metal depth being deeper than the first metal depth. The first depth supporting the first metal depth promotes metal mixing by metal convection into and out of a zone below the slag layer adjacent the vessel wall.

[0014] In yet another embodiment, the first level comprises at least 70% of the cross-sectional area of the split level refractory floor.

[0015] In yet another embodiment, the first depth supports a first metal depth of 900 mm or less.

[0016] Also according to one embodiment, the first depth supports a first metal depth of 700 mm or less.

[0017] In yet another embodiment, the first depth supports a first metal depth of 600 mm or less.

[0018] In yet another embodiment, the second depth supports a second metal depth that is at least 300 mm deeper than the first metal depth.

[0019] In yet another embodiment, metal mixing is promoted by injecting gas directly into the smelting vessel using one or more gas bubbling devices to promote metal convection to a zone below the slag layer adjacent the vessel wall.

[0020] In yet another embodiment, the gas comprises argon gas or nitrogen gas.

[0021] Also according to one embodiment, metal mixing is promoted by using one or more pairs of solids injection lances within the direct smelting vessel, with one branch of the pair of solids injection lances delivering at least a majority of the feed solids injected by the pair of solids injection lances at any given time.

[0022] In yet another embodiment, the injection of feed solids through one branch of a pair of solids injection lances is interchanged with the opposite branch of the pair of solids injection lances either immediately after injection through one branch or after a period of time.

[0023] Another embodiment of the present disclosure includes an apparatus for directly smelting metal-bearing material to produce molten metal and molten slag. The apparatus includes a direct smelting vessel having at least one of a split-level refractory hearth, a refractory hearth with one or more gas bubbling devices, or one or more pairs of solid injection lances. The split-level refractory hearth with two refractory floor levels includes a first level having a first depth supporting a first metal depth and a second level having a second depth supporting a second metal depth. The second metal depth is deeper than the first metal depth. The pair or pairs of solid injection lances are utilized such that at any one time, one branch of the pair of solid injection lances delivers at least a majority of the feed solids delivered by the pair of solid injection lances. The split-level refractory hearth, the one or more gas bubbling devices, or the pair or pairs of solid injection lances promote metal mixing in a zone below the slag layer adjacent to the vessel wall of the direct smelting vessel.

[0024] Additionally, according to one embodiment, metal mixing reduces stagnant areas that can support a semi-solid slag layer that limits metal-to-slag heat transfer between the molten metal and the molten slag.

[0025] In yet another embodiment, metal mixing maintains an effective temperature difference between the tapped metal in the forehearth and the metal at the vessel wall of 40° C. or less.

[0026] In yet another embodiment, the direct smelting vessel comprises a split-level refractory hearth.

[0027] In yet another embodiment, the first level comprises at least 70% of the cross-sectional area of the fire-resistant floor, the first depth supporting a first metal depth that is 900 mm or less, and the second depth supporting a second metal depth that is at least 300 mm deeper than the first metal depth.

[0028] In yet another embodiment, the direct smelting vessel comprises a refractory hearth having one or more gas bubbling devices.

[0029] In yet another embodiment, the direct smelting vessel includes one or more pairs of solids injection lances.

[0030] To the accomplishment of the foregoing and related ends, the one or more embodiments of the invention comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth certain illustrative features of the one or more embodiments. These features are indicative of but a few of the various ways in which the principles of the various embodiments may be employed, and the description is intended to include all such embodiments and their equivalents.

[0031] The invention will now be further described, by way of example only, with reference to the accompanying drawings in which: [Brief explanation of the drawings]

[0032] [Figure 1A-1B] Figure 1A is a cross-sectional side view of a direct smelting vessel having an SRV that uses a shallow bath concept to achieve metal mixing in the cold shoulder region according to one embodiment of the present disclosure. Figure 1B is a cross-sectional top view of the direct smelting vessel of Figure 1A according to one embodiment of the present disclosure. [Figure 2A-2B]Figure 2A is a cross-sectional side view of a direct smelting vessel having an SRV using agitating gas input to achieve metal mixing in the cold shoulder region according to one embodiment of the present disclosure. Figure 2B is a cross-sectional top view of the direct smelting vessel of Figure 2A according to one embodiment of the present disclosure. [Figure 3] FIG. 1 is a process flow diagram for direct smelting utilizing a direct smelting vessel having an SRV that employs a means for providing metal mixing in a cold shoulder zone according to one embodiment of the disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0033]

[0023] Embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. The drawings illustrate some, but not all, embodiments of the present invention. Indeed, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like reference numerals refer to like elements throughout the specification.

[0034] The term "smelting" is understood herein to mean a thermochemical process that produces molten metal containing carbon by chemical reactions that reduce metal oxides. These smelting reactions occur only when the oxygen potential is sufficiently low and are highly endothermic, requiring a large heat input to maintain a constant process temperature.

[0035] Two processes for the direct smelting of metalliferous materials that primarily use a molten bath as the smelting medium are commonly referred to as the HIsmelt and HIsarna processes. As described in more detail herein, the HIsmelt process utilizes an SRV, while the HIsarna process utilizes an SRV with a CCF positioned above the SRV.

[0036] The HIsmelt process involves the direct smelting of metal-bearing material in the form of iron oxide to produce molten iron. The process involves forming a bath of molten iron and slag in a vessel (e.g., an SRV). The material is introduced into a bath containing the metal-bearing material (e.g., iron oxide) and a solid carbonaceous material (e.g., coal), which acts as a reducing agent for the iron oxide and an energy source to form a molten metal bath in the vessel.

[0037] The HIsmelt process also involves post-combustion reaction gases, such as CO and H2, released from the bath, together with an oxygen-containing gas (usually hot oxygen-enriched air or technically pure cold oxygen) in a generally gas-continuous space above the bath (e.g., called the headspace). Heat generated by the post-combustion reactions is transferred to the bath to meet the thermal energy requirements for smelting the metalliferous material.

[0038] The HIsmelt process also involves creating a transition zone above the nominal stationary surface of the bath. In this zone, a large volume of rising and falling droplets and splashes, or a stream of molten metal and / or slag, exists, providing an effective medium for transferring a significant portion of the thermal energy generated by the post-combustion reaction gases above the bath to the bath. This jet transfers heat from the headspace where it is generated (e.g., a relatively high oxygen potential) to the bath where it is used for smelting purposes (e.g., a relatively low oxygen potential). In this way, the jet functions as a de facto heat pump.

[0039] In the HIsmelt process, metalliferous and solid carbonaceous materials are introduced into the molten bath through several solid injection lances. The lances may be vertically inclined, extending downward and inward through the sidewall of the direct smelting vessel to reach the lower region of the vessel, so that at least a portion of the solid materials are delivered to the molten metal layer at the bottom of the vessel. To promote post-combustion of the reaction gases in the upper part of the vessel, hot air, which may be cold oxygen or oxygen-enriched, is introduced into the upper region of the vessel through one or more downwardly extending gas injection lances. Offgas resulting from the post-combustion of the reaction gases in the vessel is removed from the upper region of the vessel through an offgas duct. The vessel also includes slag-coated, water-cooled panels on the sidewalls and roof of the vessel, through which water circulates in a continuous circuit.

[0040] The molten metal product is removed from the smelting and reduction vessel (SRV) through a forehearth, a siphon-type overflow device connected to the metal bath through an opening ("forehearth connection") near the bottom of the bath within the SRV. The forehearth allows molten metal to be continuously extracted from the SRV during operation while maintaining the metal level within the SRV at a level that allows safe operation (e.g., keeping the bulk metal well away from the water-cooled elements).

[0041] As far as the SRV is concerned, the HIsarna process has the same or similar physical components and layout as the HIsmelt process and operates in the same or similar manner. The difference is that in the HIsarna process, the iron ore input is not fed into a bath; instead, it is heated, partially pre-reduced, and mostly melted in a smelting cyclone (e.g., in a CCF) directly connected to the top gas outlet of the SRV. The mostly molten, partially reduced iron ore droplets fall from the smelting cyclone into the SRV slag, from which smelting proceeds (e.g., primarily carbon-rich metals react with FeO in the slag). Carbonaceous material is still fed into the bath as described above to carbonize the metal and create splashes, jets, and mixing within the SRV.

[0042] In both the HIsmelt and HIsarna processes, the heat transfer process from the top space combustion region to the bath actually occurs in two stages. The first stage is from the gas space to the slag in the upper region of the SRV, and the second stage is from the slag to the metal in the lower region. There are essentially two jets within the SRV. First, a jet of primarily slag flows into the top space, acquiring heat from the hot combustion gases. Second, a jet of metal flows into the slag layer, acquiring heat from the hot slag and transferring it to the metal bath.

[0043] This previously unrecognized mechanism that limits metal-slag heat transfer is referred to herein as the "cold shoulder." As the slag strikes the water-cooled panel, an intermediate semi-solid layer forms between the frozen layer of solidified slag and the bulk molten slag. This semi-solid layer can move downward due to gravity until it reaches the metal-slag interface near the vessel wall. If the temperature of the molten metal at this location is low enough, the semi-solid slag can float inward from the vessel wall toward the center. This layer of semi-solid slag thus occupies a portion of the cross-section of the bath, preventing free movement of the metal and slag across this horizontal interface. This limits metal-slag heat transfer and, consequently, reduces SRV productivity. The term "cold shoulder" refers to the metal temperature at the periphery of the bath. The lower this temperature, the more likely the semi-solid slag is to float inward (and the more limited metal-slag heat transfer).

[0044] Ideally, the metal and slag temperatures are reasonably close, with the slag being slightly hotter than the metal. A typical metal forehearth temperature target is 1400–1450°C (2252–2642°F). Temperatures are reduced by 20°C (36°F) from the nominal value throughout the forehearth. This suggests that the actual metal temperature in the main splash zone is approximately 1420–1470°C (2588–2678°F). The slag temperature in the main splash zone will be slightly higher, ideally 1430–1500°C (2606–2732°F), as measured during slag tapping from the slag notch. The stronger the cold shoulder effect, the greater the temperature difference between the metal and slag. A good (practical) target for efficient SRV process operation is a temperature difference of approximately 70°C (126°F) or less between the tapping temperature and the forehearth metal temperature. This corresponds to a metal-to-slag temperature differential of approximately 50°C (90°F) inside the SRV.

[0045] The present invention relates to improved metal-to-slag heat transfer through measures (e.g., passive or active) to improve metal mixing in a zone below the slag layer adjacent the vessel wall of a direct smelting vessel (e.g., the cold shoulder zone). For example, providing improved metal mixing in this zone reduces stagnant areas that can support a semi-solid slag layer that limits metal-to-slag heat transfer. In particular, the measures for providing metal mixing maintain an effective temperature difference between the tap metal of the forehearth and the metal at the vessel wall at 40°C (72°F) or less (or, in some embodiments, 30°C, i.e., 54°F, or less, or any value between 30 and 40°C).

[0046] In some embodiments of the present invention, the means for promoting metal convection may comprise a split-level refractory hearth including two refractory bed levels. As described in further detail herein, the effective depth of the metal bath in the first level provides passive metal convection in the cold shoulder zone of the SRV while also maintaining safety features around the forehearth using the second, deeper level.

[0047] In another embodiment of the present invention, the means for promoting metal convection may comprise a refractory hearth utilizing one or more gas bubbling devices.

[0048] Alternatively, at least one pair of solids input lances may be provided, with a first opposing lance of the pair delivering the input feed solids (e.g., all, most, etc.) of the pair at any time (e.g., immediately or after a period of time) before switching over to a second opposing lance of the pair, as described in more detail herein.

[0049] In the HIsmelt pilot plant, a vertical SRV was operated in a furnace with an internal diameter of 2.7 m (approximately 8.9 ft) and a metal bath depth of approximately 250–400 mm (approximately 10–16 in). The metallurgical performance of this HIsmelt process demonstrated a high heat transfer coefficient between the metal and slag, transferring up to approximately 30 MW of useful heat to the metal bath. As a result, this process converted 15 t / h of hydrous ore (62.8% iron) to 8.5 t / h of hot metal (4% carbon). Operationally, the pilot plant SRV was determined to be highly responsive to changes in the coal and ore feed rates. The temperature difference between the tapped metal and the tapped slag was small, typically between approximately 0°C and approximately 40°C (72°F). However, it is difficult to accurately measure the temperature difference within the SRV. During testing, it was determined that increasing the coal and iron ore input rates increased splash (e.g., both slag in the gas and metal in the slag) and increased heat transfer to the bath. Therefore, it was determined that the pilot plant SRV was operating in the "sweet spot" process, which was then used as justification for building a commercial-scale demonstration plant, i.e., a 6 m (approximately 19.7 ft) SRV.

[0050] One practical concern with the pilot plant SRV (2.7 m) was that the metal bath was relatively shallow, so the height of liquid metal required to create a liquid seal at the top of the forehearth connection was small (typically 150-250 mm / 6-10 in). If the backpressure control valve failed, the pilot plant SRV pressure would momentarily increase, potentially causing slag to be blown out of the forehearth. This created a potential hazard and forced the process to be shut down.

[0051] As a practical solution, all subsequent SRVs (e.g., the 6 m SRV) were designed to operate with deeper metal baths to minimize the possibility of slag blow-off. Subsequent designs used metal baths approximately 1200–1500 mm (47–59 in) deep for the 6 m SRV and approximately 850–1000 mm (34–39 in) deep for the 2.7 m Pilot Plant SRV. This deeper metal bath was very effective in reducing the possibility of slag blow-off from the forehearth connection, but it may have had unforeseen adverse effects. During commissioning of the 6 m SRV, heat transfer from the gas to the slag was very effective (e.g., the slag heated to 1500–1550 °C / 2732–2822 °F), but heat transfer from the slag to the metal bath was not as effective (e.g., the metal was only about 1400 °C / 2552 °F). Furthermore, improving heat transfer from the slag to the metal bath was difficult. The temperature difference between the tapping metal and the tapping slag was typically around 100–150°C (180–270°F), and in some cases even more than 200°C (360°F). As a result, heat transfer to the bath was limited, significantly impacting productivity and efficiency. This was thought to be a function of the solids injection lance configuration, but changes to the lance arrangement (e.g., from eight lances to two "megalances") only slightly alleviated the problem, leaving it essentially unresolved.

[0052] A slag drain test was conducted on a 6-m SRV. During normal SRV operation, a tap hole was opened in the sidewall at the metal-slag interface, followed by temperature measurements and tap metal and slag sampling. Results indicated that the metal / slag temperature at the slag drain tap hole was approximately 150°C (270°F) lower than the normal tap temperature (e.g., at the top of the slag notch) and approximately 50°C (90°F) lower than the temperature of the metal tapped in the forehearth. Snap-quenched slag samples for morphology analysis were taken from both the slag notch and the slag drain. While the sample taken from the slag notch (higher and hotter) exhibited a homogeneous (fully molten) morphology, the sample taken from the slag drain showed the presence of crystalline phases, indicating that the material at this location was significantly below its liquidus temperature. This analysis confirmed the unexpected presence of low-temperature metal and slag at the periphery of the 6m SRV, just below the slag layer.

[0053] Slag impinging on the water-cooled elements in the SRV typically forms a frozen layer 20–30 mm (0.79–1.18 in) thick. As mentioned above, a transition zone exists between the solid slag within the frozen layer and the hot, completely liquid slag away from the frozen layer. This transition zone is believed to contain highly viscous, semi-solid slag (e.g., a mixture of solid and viscous slag) containing crystalline phases consistent with precipitation from the bulk slag. Furthermore, this type of semi-solid slag is believed to slowly move downward along the wall due to gravity, eventually reaching the metal-slag interface. At this location, the semi-solid slag may effectively float above the molten metal. The material collected in the slag drain test is believed to have been collected from the semi-solid slag located at the metal-slag interface.

[0054] The presence of semi-solid slag at the metal-slag interface indicates a more serious potential problem: the temperature of the metal adjacent to the semi-solid slag is also below the desired temperature. The bulk metal temperature in the bath (e.g., the temperature measured in the forehearth plus an estimated heat loss of approximately 20°C (36°F) in the forehearth itself) was estimated to be approximately 70°C (126°F) higher than the metal adjacent to the semi-solid slag at the slag drain taphole location. This suggests that the top of the metal bath at the periphery near the vessel wall is approximately 70°C (126°F) cooler than the bulk metal (e.g., molten mixed metal) in the center (e.g., central zone) of the SRV.

[0055] Analysis of metal bath fluid dynamics suggests that mixing is related to the depth of the metal in the cold shoulder zone. Solids injection results in a more or less central metal jet zone, with a turbulent zone surrounding the central injection active area. To maintain continuity, metal extruded upward in the central zone of the SRV is locally displaced by metal entering from elsewhere. In deep baths, this metal displacement flow can come from the sides and below, consistent with normal liquid flow in large volumes of liquid. Under these conditions, the upper periphery, or cold shoulder zone, does not necessarily participate in mixing and can become a stagnant "dead spot" (with little or no mixing). This limited metal movement into and out of the cold shoulder zone can result in some localized metal cooling due to natural heat loss from the refractory wall, potentially causing the results observed in the slag drain tests.

[0056] In a shallow metal bath such as the pilot plant SRV (i.e., the 2.7 m SRV), metal displacement from below is less likely (e.g., because the floor gets in the way) and instead occurs more strongly from the side. Therefore, in the pilot plant SRV, the liquid turbulence zone associated with the injection jet is "squashed" from below, and naturally, the turbulent metal flow region is likely to expand laterally toward the vessel wall. As a result, metal convection into and out of the cold shoulder zone is significantly intensified, increasing the metal temperature in this zone. Therefore, the highly viscous, cold semi-solid slag (e.g., comprising both solid and viscous slag) in the transition zone moving down the wall will reach a metal layer that is much hotter than the slag liquidus temperature.

[0057] As previously mentioned, semi-solid slag (e.g., viscous slag with solids content) that reaches the metal-slag interface, if kept cool enough, forms a scum layer floating above the molten metal and penetrates as deep as possible toward the center of the SRV. At some point along a radial line from the wall toward the center, metal mixing and temperature rise occur sufficiently that the scum layer containing the semi-solid slag breaks down, melts, and moves (convects or mixes). The scum layer is thus in dynamic equilibrium in the form of a donut-shaped ring (in plan view) with a predetermined average size. The outer diameter of the ring is defined by the SRV wall, while the inner diameter of the ring is defined by the local metal mixing and temperature across the metal-slag interface.

[0058] This scum layer (e.g., doughnut-shaped) can provide a barrier that effectively reduces metal-to-slag heat transfer. Within the outer region, the "scum radius," this barrier effectively restricts the free upward and downward movement of liquid metal and slag. The smaller the scum radius, i.e., the smaller the radial distance from the outer wall to the point where the scum breaks, melts, and moves, the easier it is for the bulk metal and bulk slag layer within the SRV to interact and exchange heat. The smaller the scum radius is believed to be the reason why the pilot plant SRV (i.e., 2.7 m) performed better than the 6 m SRV in terms of slag-to-metal heat transfer.

[0059] A key problem identified is that metal stagnation in the cold shoulder zone leads to localized cooling, resulting in a larger scum layer than would occur without cooling. To improve metal-slag heat transfer efficiency in large SRVs (e.g., deep metal SRVs), metal mixing (e.g., passive and / or active) in the cold shoulder zone should be promoted. As described herein, mixing in the cold shoulder zone can be improved in several ways by various means. However, the primary objective is to introduce a sufficient amount of hot bulk molten metal into the cold shoulder zone to break up, mix, and melt the scum layer and expand the central "active core" zone for free metal-slag mixing and heat transfer.

[0060] As described herein, means for promoting metal mixing (e.g., passive mixing and / or active mixing) in the cold shoulder zone may include (i) a split-level refractory hearth having two refractory bed levels, (ii) a refractory hearth utilizing one or more gas bubbling devices, and / or (iii) at least a pair of solids input lances that deliver input solids to the pair at any time before a first opposing lance of the pair switches over to a second opposing lance of the pair.

[0061] For split level refractory hearths, passive radial metal mixing is promoted by making the majority of the SRV metal bath sufficiently shallow while maintaining deep bath zones adjacent to the forehearth connection and end drain taphole for safety reasons (as per the pilot plant 2.7m SRV).

[0062] Alternatively or additionally, additional stirring gas may be intentionally introduced into the bath by suitable means to promote metal mixing near the wall and achieve the required heat transfer results.

[0063] Further, alternatively or additionally, the method may deliberately use a pair of one-sided solid injection lances that create jets of sufficient strength to promote the necessary convection levels in the metal layer at the opposing wall. In this manner, a strategy of alternating opposing lances (a given pair) on a regular cycle can be used to control the scum layer, using the relatively long time constant required for the hot metal in the wall region to cool sufficiently before a scum layer forms again in a significant way.

[0064] Referring to the drawings, Figure 1A shows a side cross-sectional view of a direct smelting vessel 101 that forms part of a plant particularly suitable for operation using the HIsarna process described herein. Figure 1B also shows a top cross-sectional view of the direct smelting vessel 101 of Figure 1A. As shown in Figure 1A, a layer of molten slag 102 is located above a layer of molten metal 103 and is supported by a refractory-lined hearth 104 within an SRV 120.

[0065] The direct smelting vessel 101 utilizes two solids injection lances 105 to inject coal and additives into the molten metal bath so that they enter the molten metal layer 103 and form a turbulent injection zone 106. The bottom of the injection zone 106 is determined by the conditions at the outlet of the injection lances 105 and is typically located approximately 200 to 300 mm (7.9 to 11.8 inches) below the quiescent metal level in the SRV 120.

[0066] The hearth bottom shown in FIG. 1A includes two distinct levels. For example, the main level (or "first level") may comprise 60, 65, 70, 75, 80, 85, 90, 95 percent, or a range of percentages (e.g., percentages including, exceeding, or overlapping these values) of the planar area (cross-sectional area) of the refractory hearth, although the main level (or "first level") may also comprise a higher floor level. In certain embodiments, when the main level is the higher floor level, its area is preferably at least 70%. In other embodiments, when the main level is the higher floor level, its area is in the range of about 75-85%, and in some embodiments, it is preferably about 80%. The remaining percentage of the hearth floor area is a secondary level (or "second level") deeper than the main level and adjacent to the forehearth connection 109. In certain embodiments, the percentage of the secondary level ranges from 15 to 25% of the refractory hearth floor area, and in some embodiments, is preferably about 20%. The bed height of the main level may be selected so that the working metal depth 107 is no more than about two times the calculated metal input depth from the lance input jet. In practice, this height corresponds to a metal bath depth of about 400 to 600 mm (about 15.7 to 23.6 inches) in a commercial-scale SRV (e.g., a 6 m SRV). It should be understood that the bath depth may vary based on the diameter of the refractory hearth (e.g., scaled for diameter changes). Therefore, the depth ratios described herein can be used to scale the depth for different SRVs having different diameters.

[0067] The floor height of the secondary level can be set to meet safety requirements related to maintaining a forehearth seal (e.g., 1200–1500 mm, or 47.2–59.1 in., for a commercial-scale 6-m SRV). The secondary level can be sized to function as a metal sump that accommodates both the forehearth connection 109 and one or more end-drain tapholes 110. With this type of refractory furnace configuration, strong lateral metal mixing into the cold shoulder zone occurs naturally (e.g., passively, from the plant operator's perspective). This provides the "meltback" necessary to keep the scum layer small and allows free metal-slag interaction for heat transfer. This results in reduced FeO in the slag, improved productivity, increased efficiency, and reduced costs. For slag formulations where bulk foaming is a potential issue (e.g., iron ore containing 2–6% titania), the likelihood of foaming is also reduced, allowing for more reliable SRV operation.

[0068] 2A and 2B show SRV201 with a conventionally constructed refractory bed having a metal bath depth of approximately 1200 to 1500 mm (approximately 47.2 to 59.1 inches) across the entire diameter of the 6 m SRV.

[0069] 2A and 2B, some embodiments of the present invention may utilize a series of downwardly sloping bubbling lances 202 to mix the molten metal within the SRV, particularly to promote mixing in the cold shoulder zone. The bubbling lances 202 deliver a bubbling stirring gas (e.g., argon gas) into the metal bath, which promotes gas stirring in the molten metal (e.g., similar to the use of gas bubbling to promote mixing in a ladle).

[0070] Gas bubblers 202 (e.g., argon bubblers) are typically thick-walled stainless steel tubes with an inside diameter (ID) of approximately 5 mm (approximately 0.20 in.) and an outer alumina layer approximately 5-15 mm (approximately 0.20-0.59 in.) thick. These bubblers are designed so that if back pressure is lost for any reason, the molten metal will attempt to backflow into the bubbler, where it will freeze (e.g., due to the large heat capacity of the tube wall compared to that of the liquid metal). This allows for an inherently fail-safe design, where failure of the bubbler will not compromise the remaining refractory lining.

[0071] The bubbler provides an active metal mixing impulse to the otherwise stagnant cold shoulder zone, providing benefits similar to those described for the main and secondary levels of the split level refractory hearth.

[0072] In some embodiments, a pair of unilateral solids injection lances is used, each with an injection jet strong enough to promote convection in the metal layer on the opposing wall. This strategy of alternating opposing lances (in a given pair) in a regular cycle can be used to control the scum layer, using a relatively long time constant for the hot metal in the wall area to cool sufficiently before a significant scum layer forms again. Therefore, at least one pair of opposing solids injection lances can be utilized, with substantially all of the bath input feed solids assigned to each pair being delivered through one branch of that pair at any given time (e.g., at least 50% of the total time of normal operation). Following delivery through one branch of each lance pair, a switch is made to the other branch immediately after or some time after the period through the previous branch. This asymmetric lance delivery, combined with the thermal inertia of the metal, can achieve advantages similar to those described above with respect to the main and secondary levels of a split-level refractory hearth and / or gas bubblers. It should be understood that delivering substantially all of the feed solids may include all or a negligible amount of the solids delivered by the opposing lances. Additionally, in some embodiments, a majority of the feed solids may be allocated to one of a pair of opposing lances, such that in some embodiments, the feed solids delivered from one branch of a pair of opposing lances may comprise 99, 98, 97, 96, 95, 94, 93, 92, 91, 90, 85, 80, 75, or an equivalent percentage of the feed solids delivered by that pair of opposing lances.

[0073] In some embodiments, different means for promoting metal mixing in the cold shoulder zone may be used in combination. For example, certain means may include one or more of the SRV having a main level and a secondary level described with respect to Figures 1A and 1B, the use of bubblers 202 to provide improved melting in the cold shoulder zone, the use of at least one pair of opposed solids injection lances and alternating solids feed between each lance of the pair, and / or the use of other similar means not specifically described herein.

[0074] A molten bath-based method for directly smelting metal-bearing material, such as iron oxide, in a direct smelting vessel to produce molten metal is shown in Figure 3. As shown in block 310 of Figure 3, metal-bearing material (e.g., ore such as iron ore fines) is introduced into the SRV 120 using a solid lance 105 and / or into a smelting cyclone 130 leading to the SRV 120.

[0075] In some embodiments, an ore pre-treatment unit, such as an ore dryer or ore pre-heater, may be utilized to dry and / or heat the solid metalliferous material before it is introduced into the SRV 120 through the injection lance 105 or into the smelting cyclone 130. Additionally, a metalliferous material distribution / metering unit may be utilized to control the timing and amount of metalliferous material used for the pre-treated metalliferous material.

[0076] 3, block 320 indicates that solid carbonaceous material (e.g., coal, etc.) is introduced into the molten bath within the SRV 120 via at least one injection lance (e.g., extending downward and inward, etc.) such that the introduced solids at least partially penetrate the molten metal layer. Additionally, a carbonaceous material dispensing / metering unit may be utilized for the carbonaceous material to control the timing and amount of carbonaceous material used.

[0077] 3 further illustrates that a means for promoting metal mixing in the cold shoulder zone adjacent the wall and below the slag layer is utilized to control the scum layer as described herein at block 330. The means for promoting metal mixing is used to maintain the metal in the cold shoulder zone at a temperature that is up to 40° C. (72° F.) lower than the temperature of the metal in the SRV forehearth, or other temperature as described herein.

[0078] As illustrated at block 330, the method includes using a split-level refractory hearth as described herein to promote passive radial metal mixing while maintaining a deep bath zone adjacent the forehearth connection.

[0079] Alternatively or additionally, measures include the deliberate introduction of additional stirring gas into the bath, such as by a gas bubbler, to promote metal mixing near the walls of the SRV and achieve slag-to-metal heat transfer.

[0080] Alternatively or additionally, the method involves the deliberate use of a pair of one-sided solid injection lances with injection jets strong enough to promote convection in the metal layer on the opposing wall. By alternating between a given pair of opposing lances in a regular cycle, the formation of the scum layer can be controlled using the relatively long time constant required for the hot metal in the wall region to cool sufficiently before a scum layer forms again in a significant way.

[0081] To supplement this disclosure, this application incorporates the following documents, each of which is incorporated herein by reference in its entirety: 1. U.S. Patent No. 6,989,042, "Direct Smelting Process and Apparatus," Priority Date: April 17, 2000 2. U.S. Patent No. 8,221,675, "Direct Smelting Vessel and Cooler Therefor," Priority Date: May 18, 2006 3. U.S. Patent No. 9,175,907, "Direct Smelting Process and Apparatus," Priority Date: February 9, 2010 4. Australian Patent No. 2011301784 (WO2012 / 034184) "Direct Smelting Process" Priority Date: September 15, 2011 5. U.S. Patent No. 9,359,656, "Direct Smelting Process," Priority Date: February 9, 2012 6. PCT / AU2012 / 000293 (WO2012 / 126055) "Direct Smelting Process for High Sulphur Feed" Priority Date: March 21, 2012 7.PCT / AU2012 / 001486(WO2013 / 082658) "Starting a Smelting Process" Priority date December 6, 2011 8.PCT / AU2012 / 001481(WO2013 / 082653) "Starting a Smelting Process" Priority date December 6, 2011 9.PCT / AU2012 / 001487(WO2013 / 082659) "Starting a Smelting Process" Priority date December 6, 2011 10. PCT / AU2014 / 001098 (WO2015 / 081376) "Smelting Process and Apparatus" Priority Date: December 4, 2014 11. PCT / AU2014 / 001146 (WO2015 / 089563) "Smelting Process and Apparatus" Priority Date: December 19, 2014

[0082] Specific embodiments of the invention have been described herein. Many modifications and other embodiments of the inventions described herein will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. It is to be understood that the invention is not limited to the specific embodiments disclosed, and that all modifications, other embodiments, and combinations of the embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. 1. A method for directly smelting a metalliferous material in a direct smelting vessel to produce molten metal, comprising: injecting solid carbonaceous material through at least one injection lance extending into the direct smelting vessel, the solids being injected so as to at least partially penetrate a layer of molten metal in the direct smelting vessel, with a layer of slag floating above the layer of molten metal; promoting metal mixing in a zone immediately below the slag layer adjacent a vessel wall of the direct smelting vessel; A method comprising:

2. 10. The method of claim 1, wherein the metal mixing reduces the volume occupied by stagnant regions of low temperature sufficient to support a semi-solid slag layer that limits metal-to-slag heat transfer.

3. 10. The method of claim 1, wherein the metal mixing maintains an effective temperature difference between the forehearth tap metal and the metal at the vessel wall of 40°C or less.

4. The metal mixing is facilitated using the direct smelting vessel, the direct smelting vessel comprising: a split-level refractory floor having two refractory floor levels including a first level having a first depth supporting a first metal depth and a second level having a second depth supporting a second metal depth; the second metal depth is greater than the first metal depth; a first depth supporting a first metal depth to promote metal mixing by metal convection into and out of a zone below the slag layer adjacent the vessel wall; The method of claim 1.

5. 5. The method of claim 4, wherein the first level comprises at least 70% of the cross-sectional area of the split-level refractory floor.

6. 5. The method of claim 4, wherein the first depth supports a first metal depth that is 900 mm or less.

7. The method of claim 4 , wherein the first depth supports a first metal depth that is 700 mm or less.

8. 5. The method of claim 4, wherein the first depth supports a first metal depth that is 600 mm or less.

9. The method of claim 4 , wherein the second depth supports a second metal depth that is at least 300 mm deeper than the first metal depth.

10. 10. The method of claim 1, wherein the metal mixing is promoted by injecting gas into the direct smelting vessel using one or more gas bubbling devices to promote metal convection into the zone below the slag layer adjacent the vessel wall.

11. The method of claim 10 , wherein the gas comprises argon gas or nitrogen gas.

12. 2. The method of claim 1, wherein the metal mixing is facilitated by using one or more pairs of solids injection lances within the direct smelting vessel, one branch of a pair of solids injection lances delivering at least a majority of the feed solids delivered by the pair of solids injection lances at any one time.

13. 13. The method of claim 12, wherein the introduction of feed solids through one branch of the pair of solids introduction lances is interchanged with the opposite branch of the pair of solids introduction lances either immediately after introduction through the one branch or after a period of time.

14. 1. An apparatus for directly smelting a metalliferous material to produce molten metal and molten slag, comprising: a direct smelting vessel; (a) a split-level refractory hearth having two refractory floor levels, a first level having a first depth supporting a first metal depth; a second level having a second depth supporting a second metal depth; wherein the second metal depth is greater than the first metal depth; (b) a refractory hearth having one or more gas bubbling devices; or (c) one or more pairs of solids injection lances, wherein one branch of the pair of solids injection lances delivers at least a majority of the feed solids injected by the pair of solids injection lances at any one time; and 1. The apparatus of claim 1, wherein the split-level refractory hearth, the one or more gas bubbling devices, or the pair or pairs of solids injection lances promote metal mixing in a zone below a slag layer adjacent a vessel wall of the direct smelting vessel.

15. 15. The apparatus of claim 14, wherein the metal mixing reduces stagnant areas that can support a semi-solid slag layer that limits metal-to-slag heat transfer between the molten metal and the molten slag.

16. 15. The apparatus of claim 14, wherein the metal mixing maintains an effective temperature difference between the forehearth tap metal and the metal at the vessel wall of 40°C or less.

17. The apparatus of claim 14 , wherein the direct smelting vessel comprises the split-level refractory hearth.

18. 18. The apparatus of claim 17, wherein a first level comprises at least 70% of the cross-sectional area of the refractory bed, the first level supporting a first metal depth having a first depth of 900 mm or less, and the second level supporting a second metal depth having a second depth at least 300 mm greater than the first metal depth.

19. The apparatus of claim 14 , wherein the direct smelting vessel comprises the refractory hearth having the one or more gas bubbling devices.

20. The apparatus of claim 14 , wherein the direct smelting vessel comprises the pair or pairs of solids injection lances.

Images